The specific aims are: (1) to determine rate constants of photochemical and microbial degradation of selected xenobiotics such as chlorinated or nitrated aromatic compounds in freshwater and estuarine environments, (2) to determine the effects of environmental factors such as season, pH, and adaptation on rate constants of photolysis and microbial degradation of the test compounds, (3) to assess the mutagenic effects of the test compounds and their photoproducts, (4) to assess the applicability of using measurement of bacterial heterotrophic activity as toxicity indicator (and how they relate to mutagenic effects) in aquatic ecosystems, (5) to evaluate the contribution of photolysis and adaptation to microbial degradation of the test compounds and to determine the relative importance of photolysis and microbial degradation in the removal process of the test compounds, (6) to train minority students to conduct environmental and biomedical research, to analyze the experimental data, and to report the experimental results independently. The approach involves the use of simultaneous incubation systems to determine the photochemical and microbiological fates of the test compounds. In addition, the mutagenic effects of the test compounds and their photoproducts will be examined with the method of Ames. The results of mutagenicity experiments will be compared to the results of concurrent measurements of bacterial heterotrophic activities, to determine the sensitivity of the latter method in detecting the toxicity. The long-term objectives of this study are: (1) to have produced the data base for the regulatory agencies to predict persistence of the test compounds and to have provided more accurate and rapid methods to detect the toxicity of the test compounds and their photoproducts, (2) to have provided a technical service to the industrial sector which should strengthen relationships between industry and Jackson State University, and (3) to have provided both academic and practical training for minority students who upon graduation are able to compete successfully in environmentally-related graduate degree programs.